Phase noise measurement of semiconductor optical amplifiers

Abstract

We introduce a novel measurement method for the phase noise measurement of optical amplifiers, topologically similar to the Heterodyne Mach-Zehnder Interferometer but governed by different principles, and we report on the measurement of a fibered amplifier at 1.55 $\mu \mathrm{m}$ wavelength. The amplifier under test (DUT) is inserted in one arm of a symmetrical Mach-Zehnder interferometer, with an AOM in the other arm. We measure the phase noise of the RF beat detected at the Mach-Zehnder output. The phase noise floor of the amplifier decreases proportionally to the reciprocal of the laser power at the amplifier input, down to $-125$ $\mathrm{dBra}{\mathrm{d}}^2/Hz$ at $f=100$ $\mathrm{kHz}$. The DUT flicker noise cannot be measured because it is lower than the background of the setup. This sets an upper bound of the amplifier noise at $-32$ $\mathrm{dBra}{\mathrm{d}}^2/Hz$ at $f=1$ $\mathrm{Hz}$, which corresponds to a frequency stability of $5.2\times 10^{-17}/\tau$ (Allan deviation), where $\tau$ is the integration time. Such noise level is lower than that of most Fabry-Perot cavity-stabilized lasers. These results are of interest in a wide range of applications including metrology, instrumentation, optical communications, or fiber links.

7 pages, two-column IEEE format, 5 figures, 52 references

References in corpus (7)

• A clock with $8\times 10^{-19}$ systematic uncertainty
• Roadmap towards the redefinition of the second
• High-performance, compact optical standard
• Tackling the Limits of Optical Fiber Links
• Applications of the optical fiber to the generation and to the measurement of low-phase-noise microwave signals
• The Companion of Enrico's Chart for Phase Noise and Two-Sample Variances
• Phase noise characterization of sub-hertz linewidth lasers via digital cross correlation